Theoretical study of the atomic and electronic structure of grain boundaries in SiC

The atomic and electronic structure of a typical coincidence tilt boundary in cubic SiC, the {122}Sigma=9 boundary, has been examined theoretically using the first-principles calculations based on the density-functional theory. Results are compared with recent electron microscopy observations. We have obtained the stable configurations for the N-type polar, P-type polar and non-polar interfaces, which have different interface stoichiometries and different numbers of Si-Si or C-C wrong bonds. The relative stability among the interfaces has been analyzed by calculating the thermodynamic potentials as a function of the atomic chemical potentials. The relative stability of the zigzag model against the straight model for the nonpolar interface has been shown, which can well explain the high-resolution electron microscopy observation of the triple junction of the Sigma=9 and Sigma=3 boundaries. Effects of wrong bonds on the electronic structure have been analyzed through the electronic structures of the interfaces and antisite defects, which are consistent with electron energy-loss spectroscopy observations.